Dental enamel is the outermost layer of the teeth. The fully developed mature dental enamel is made of enamel prisms, highly organized micro-architectural units, which have bundles of nanorod-like calcium hydroxyapatite (HA) crystals arranged roughly parallel to each other. This structure spans the entire enamel thickness and is likely to play an important role in determining the unique physico-chemical properties of the enamel.
Dental caries is a widespread, chronic, infectious disease experienced by almost 80% of children in the US by the age of 18 and by more than 90% of adults. Such a phenomenon is not restricted to the U.S., but rather is prevalent throughout the world. Caries is, in fact, considered to have a multifactorial etiology. The most prevalent way in which dentists treat carious tissue is to remove it surgically, resulting in an extensive cavity and loss of structural integrity of the tooth. The current standard of care for carious lesions in the dentin is invasive operative treatment. This means removal of all carious dentin (removal of all diseased tissue) and replacement by a restoration to restore form, function, and integrity of the tooth. The great number of such treatments also suggests that existing techniques have only limited success and that there will be an ongoing need for restoration of carious lesions, whether primary or secondary in nature. This operative treatment option is time-consuming to both dentists and patients, and costly. Worldwide, the placement, replacement, and repair of restorations in teeth account for anywhere from 30-70% of a dentist's activity. In order to reduce the cost of oral care to both the patient and governmental bodies, there is a need for the development of new anti-caries restorative products and materials.
Dentin hypersensitivity results when protective enamel or cementum covering dentine is lost. Cementum is easier to breach than enamel, because cementum is thinner and more easily eroded by acids. However, breach of cementum cannot happen until there is gingival recession and exposure of the root surface to the oral milieu. Individuals with breached cementum and suffering with dentinal hypersensitivity often experience pain when the exposed area of the tooth comes into contact with cold air or hot and cold liquids or foods that are sweet or acidic or is touched with a metal object.
One way that loss of cementum occurs (and the same is true of enamel) is by the process of dental caries. Acids are produced as end-products of the bacterial degradation of fermentable carbohydrate and these acids dissolve hydroxyapatite, which, like dentin and enamel, is the main calcium phosphate mineral that comprises most of the mineral of the cementum. Another source is acidic foods which, if ingested frequently and for prolonged periods of time, will cause tooth demineralization. These include fruit juices and many beverages, both alcoholic and non-alcoholic. Other acidic agents leading to chemical erosion include various oral personal care products. Amongst these are many of the commercially available mouthwashes and some toothpastes. Abrasive toothpastes and vigorous brushing can aid the erosion process. Another way in which dentin tubules lose their protective cementum and enamel coverings is through procedures performed by the dentist or hygienist in the dental office. This includes cavity and crown preparation of teeth for fillings and other restorations. It also includes cementum removal during scaling and root planing by the periodontist or dental hygienist.
Many attempts have been made with limited success to obstruct exposed dentinal tubules and to thereby reduce or stop the ability of stimuli to reach the pulp and cause pain. Materials either singly or in combination have been tried to produce an effective barrier. Blockage of the tubules through the formation of a calcium phosphate precipitate is a common approach. This includes the mixing of a soluble calcium salt with a soluble phosphate salt and immediately applying the combination to the open tubules. Alternatively, application of one salt before the other to try to get a precipitate to form within tubules is also used. There remains acute need for compositions and methods for blocking exposed dentinal tubules to treat dentinal hypersensitivity.